It is already known to use twin casings as a sensor for detecting the impact of the shell or the equivalent against targets. To obtain the twin casing, the nose, and if appropriate the sides, of the shell comprise an outer casing whose shape is determined by the requirements of air resistance, etc. In addition, there is an inner casing which often has, although not necessarily, a shape running almost parallel to the outer casing. Both casings are electrically conductive, and electrical contact arises between the casings when they are subjected to deformation. In certain applications, insulation is provided between the casings with the aid of a layer of insulating material which is placed inbetween the casings. For reasons of strength, the inner casing can be produced as an insulating casing with a metal lining. Wires can be run from the twin casing arrangement in a known manner so that the outer envelope of the shell can constitute one of the conductors and an insulated cable which is guided through the warhead to the ignition system constitutes the other conductor. Instead of having the outer envelope of the shell constitute the one conductor, the latter can, in the same way as the second conductor, be formed by an insulated cable.
Other arrangements are also known in connection with twin casing. For example, French Patent 2,294,425 describe how to arrange twin casings of the ammunition unit in an ignition system. The outer casing is separated from the inner casing by material lying between them in accordance with the above. The outer casing transmits mechanical deformation, via the material, to the inner casing which, when the deformation occurs, generates, with the aid of an electrical contact surface on its inner side, an electrical contact with contact members located within the inner casing. The contact members are arranged on electrical conductors (cables) which extend centrally inside the body. The purpose of this known arrangement is to lessen the risk of establishing contact in the event of relatively light impacts, jolts, etc., and under mechanical influences associated with handling, storage and the like.
From the U.S. Pat. No. 3,188,960 it is already known to utilize, in ignition systems, a type of sensor other than the twin casing arrangement described above. In the U.S. Pat. No. 960 the ignition system comprises cylinders which are arranged inside the ammunition-bearing unit and between which extend the rear parts of contact members substantially parallel to each other. The contact members are elongate and their front parts extend beyond the spaces between the cylinders towards the front end of the projectile where they are anchored in an internal, centrally arranged member which is included in the nose part of the projectile. The purpose of this known arrangement is to produce single contact and twin contact functions. This arrangement increases to increase the sensitivity so that initiation can take place in the event of soft targets and at large angles between the longitudinal axis of the projectile or equivalent and a line perpendicular to the target.